Since the 1870's, when Hezekiah Bradford introduced them, Bradford Breakers have been made larger and larger to meet the ever increasing demands for greater operating capacity or through-put.
Bradford's breaker was a simple device for reducing and screening coal or other materials of similar breaking characteristics and for separation of unwanted materials. It was a perforated rotatable drum or cylinder with lifter shelves inside. When you looked into one end of a clockwise rotating breaker with a bed of coal in it, you could see the lifter shelves lifting successive portions of the bed. The drum rotated relatively slowly. In general, by the time a given shelf loaded with coal reached approximately the 10 o'clock position or approached the 11 o'clock position, it had tipped far enough to drop the coal back into the bottom of the cylinder generally at about the 6 o'clock position. The impact of the fall and the abrasion of pieces of coal in the bed against each other and against the perforated drum reduced the coal. Small pieces worked their way down through the bed and the perforations, while larger pieces and foreign materials received further treatment as they progressed towards the drum outlet.
Progress has never seemed rapid in this art. For about a half century after it was introduced, the form and operation of the Bradford Breaker changed little. Some improvements were however made during this period on details of shelf and drum design.
Perhaps the most significant improvement occurred in the late 1920's. George W. Borton, as described in his U.S. Pat. No. 1,784,983, mounted in the drum of the Bradford Breaker a rotor structure carrying hammers of the type previously used in rotary beaters or hammer crushers. The rotor was placed on the center line of the drum in such a position that materials falling off the shelves dropped in the path of the rapidly rotating hammers.
Borton recognized that one needed to select a proper speed for the drum so that the shelves would carry the material to the proper height before dropping it in the rotor. And he had a definite objective in mind. As he taught in U.S. Pat. No. 2,108,793, the essential point was to select a speed (and therefore a dropping point) which would result in the "hammers hurling the material tangentially against the inner wall of the drum at one point of engagement, and such material rebounding from the wall of the drum at another angle and dropping into the hammer zone for further reduction, which cycle of operation will be repeated until the desired combination has been effected." He also suggested that adjustable lifting shelves be used with the same object in mind. Thus, Borton taught the principle that one should select a combination of drum speed and lifter adjustment which would emphasize hitting the dropped coal upwards with the rotor so it would rebound off the drum and back into the rotor for repeated impact.
Borton's influence continues. Up to the present day, the above-mentioned principle is the fundamental guide in the design of rotor-equipped breakers. Notwithstanding further improvements in drums, lifters and driving systems, changes in basic principles of breaker design and operation occur very slowly in this art. Commercial units now under construction, bearing a remarkable resemblance to the apparatus Borton described more than 40 years ago in U.S. Pat. No. 1,784,983, silently testify to this fact. Unaware of the principles needed for large scale improvement of breaker/crusher performance, designers and manufacturers faced with the requirement of a high through-put installation, have scaled up machines in accordance with the old principle, or have used a number of smaller machines of the old design, notwithstanding the ensuing cumbersome construction, duplication of facilities, and economic penalties.